1. Field of the Invention
The present invention generally relates to an apparatus for making diagnosis a high pressure fuel system of a cylinder injection type internal combustion engine as to whether or not the high pressure fuel system is suffering abnormality. More particularly, the present invention is concerned with an abnormality diagnosis apparatus for a high pressure fuel system of a cylinder injection type internal combustion engine for making diagnosis as to the abnormality of a spill valve which constitutes a part of the high pressure fuel system of the cylinder injection type internal combustion engine (also referred to as cylinder injection type engine or simply as the engine).
2. Background Technology
As a first hitherto known or conventional abnormality diagnosis apparatus for a high pressure fuel system of a cylinder injection type internal combustion engine, there is known an apparatus which is comprised, for example, of a pressure detecting means for detecting a pressure on a discharge side of a fuel feed pump, a control means for controlling a discharge quantity of the fuel feed pump on the basis of the detection result of the pressure detecting means so that the pressure on the discharge side of the fuel feed pump becomes equal to a desired or target pressure, and an abnormality determination or decision means for making decision that an abnormal state is prevailing when a discharge quantity control command value used for controlling the discharge quantity in the control means mentioned above becomes greater than a predetermined decision value which is not exceeded ordinarily by the discharge quantity control command value. (To this end, reference may have to be made to Japanese Patent Publication No. 2844881.)
With the first hitherto known apparatus, it is contemplated as an object thereof to detect with a high accuracy such abnormality that a sufficient or proper amount of fuel is not discharged due to the fuel leakage taking place ascribable to injuries of a fuel supply pipe or conduit, an accumulator and/or the like as well as abnormality brought about by the abnormality of the high pressure fuel pump, to thereby make it possible to take appropriate measures.
Further, as the second hitherto known or conventional apparatus, there has been proposed such an apparatus which is designed to determine the fuel leakage from a fuel feed system extending from the fuel feed pump to the fuel injector(s) of the engine on the basis of change of the fuel pressure prevailing within an accumulator during a predetermined period in which neither fuel feeding under pressure based on an amount of the fuel fed under pressure every predetermined period from the fuel feed pump when the internal combustion engine is operating nor fuel injection to individual cylinders through the fuel injections is executed (e.g. reference may have to be made to Japanese Patent Publication No. 3345933).
Further, as the third conventional apparatus, there is known an apparatus of such an arrangement in which the fuel pressure prevailing within the fuel system into which the fuel is discharged from the high pressure fuel pump and the engine rotation speed (rpm) are read, wherein when the engine rotation speed (rpm) is higher than a predetermined idling rotation speed (rpm) inclusive during a non-fuel-injection period and when the fuel pressure neither reaches nor exceeds a prescribed high pressure over a preset time or more within a predetermined time, it is regarded that there exists a possibility of abnormality taking place in the fuel system, whereby an abnormality flag is set with an abnormality lamp being lit. Besides, when it is determined that the abnormality flag is set, an on/off value interposed in a bypass passage interconnecting a discharge port of the fuel pump and the fuel tank is opened to thereby clear the pressure increase within the fuel system. (By way of example, reference may have to be made to Japanese Patent Application Laid-Open Publication No. 9028/1998 (JP-A-1998-9028).)
However, in general, as the abnormal state in which the spill valve in the high pressure fuel system becomes unmovable at the closed position, there can be mentioned an electrical abnormal state in which the spill valve becomes electrically unmovable at the closed position due to wire breaking and/or short circuit occurring in the spill valve and a mechanical or physical abnormal state, so to say, in which the spill valve becomes mechanically or physically unmovable due to admixture of foreign material(s) mixed with the fuel, wherein the electrical abnormal state can be detected with the aid of an abnormality detection circuit(s) (e.g. short circuit/breakage detection circuit) known in the art.
However, in the case where the spill valve is in the mechanical or physical abnormal state, this means that the spill valve is in the state insusceptible to being opened regardless of a valve open command issued to the spill valve from the ECU or alternatively the spill valve remains in the state fixedly secured at the closed position notwithstanding of the fact that the spill valve is undergoing the open control during the fuel discharge period of the high pressure fuel pump, indicating thus the electrically normal state. For this reason, the physical or mechanical abnormality of the fuel rail can not be detected with the conventional abnormality detection circuit.
Furthermore, as fourth conventional apparatus, there has also been proposed such an apparatus which is so designed as to monitor the behavior of the fuel pressure in the high pressure fuel system or alternatively the relation between the air-fuel ratio and the fuel injection pulse width for the fuel injector, wherein when behavior of the fuel pressure is abnormal or unless consistency is found in the relation between the air-fuel ratio and the fuel injection pulse width (i.e., when the conditions are satisfied), diagnosis can be performed with a high accuracy to the effect that the high pressure pump and a high pressure regulator which constitute parts of the high pressure fuel system are abnormal, fuel leakage from the high pressure fuel system takes place and/or that failure of opening the fuel injector occurs. (By way of example, reference may have to be made to Japanese Patent Application Laid-Open Publication No. 82134/1999 (J-P-1999-82134).
More specifically, upon diagnosis of the high pressure fuel system, when the fuel pressure of the high pressure fuel system has not attained a predetermined pressure even after lapse of a predetermined time since starting of the engine operation, or when the fuel pressure of the high pressure fuel system departs from a fuel pressure range which the fuel pressure of the high pressure fuel system can not ordinarily assume after the start of the engine operation or when the state in which the fuel injection pulse width exceeds a predetermined value has continued over a predetermined time period in the state where lean air-fuel mixture prevails (i.e., when the conditions for the abnormality decision are satisfied), the fourth conventional apparatus mentioned above diagnostically determines that the high pressure fuel system suffers abnormality.
With hitherto known abnormality diagnosis apparatus for the high pressure fuel system of the cylinder injection type internal combustion engine such as the first to fourth conventional apparatuses described above, abnormality of the high pressure fuel system can certainly be detected. However, it is impossible to identify discriminatively which location of the high pressure fuel system is in the abnormal state, giving rise to a problem.
Further, although the first to third conventional apparatus are certainly capable of detecting the abnormality of the high pressure fuel system which is primarily ascribable to the fuel leakage, these apparatuses can not detect the abnormal state of the spill valve in which the spill valve is unmovable at the closed position nevertheless of the opening control of the spill valve being carried out during the fuel discharge period of the high pressure fuel pump, incurring another problem.